Preparation of cenosphere microcapsules and their application in foam concrete

Abstract

In this study, hydrogen fluoride (HF) was used to generate perforated holes in cenospheres. The cavities of the cenospheres were then filled with coagulants (calcium chloride (CaCl2)) and encapsulated in polyvinyl alcohol to obtain cenosphere microcapsules. The release curve of the cenosphere microcapsules in deionised water was tested using ethylenediaminetetraacetic acid titrimetry, and the corresponding release mechanism was studied. Foam concrete (800 kg/m3) was prepared using the physical foaming method with 42·5R ordinary Portland cement, a vegetable protein foaming agent, fly ash, coagulant and the cenosphere microcapsules. Sample characterisation was performed using a rheometer, SEM systems and image-analysis software. The results demonstrated that the calcium chloride release rate of the cenosphere microcapsules was relatively low in the first 16 min, and that the cumulative release rate was 6·9%. The calcium chloride release rate increased after 16 min, the cumulative release rate reaching 58·4% at 32 min, after which the release rate decreased again. This 'controlled-release' phenomenon caused the cenosphere microcapsules to release only a few coagulants during the stirring and pouring stages but to release coagulants quickly during the moulding stage. Consequently, the relative viscosity of the cement slurry in the stirring and moulding stages did not increase, while the setting time of the cement paste shortened, the size stability and uniformity of the air pores in the foam concrete were enhanced, and the physical and mechanical properties of the foam concrete were improved.